Math.Abs(a - b) < some_epsilon    // `a` is roughly equivalent to `b`

public static bool DoubleEquality(double a, double b)
{
    const double epsilonValue = 1e-15;
    if (double.IsNaN(a))
        return double.IsNaN(b);
    else if (double.IsInfinity(a))
        return double.IsInfinity(b);
    else if (a == 0)
        return b == 0;
    else
        return Math.Abs(a - b) <= Math.Abs(a * epsilonValue);
}